Ecological determinants of fungal diversity on dead wood in 1

The fine-scale ecological determinants for wood-inhabiting aphyllophoroid basidiomycetes 16 were investigated with statistical analyses of the occurrence of fruit bodies on woody debris 17 collected in Switzerland and Ukraine. Three substrate descriptors were considered: diameter, 18 degree of decomposition and host tree species. 19 By means of Multiple Regression Trees, thresholds in the response of fungal communities to 20 these local environmental descriptors were detected. Three classes for diameter, as well as for 21 degree of decomposition were thus delimited. They revealed the importance of very small sizes, 22 which were not reported in the literature so far: the relevant diameter class limits were about 23 0.72 cm and 1.35 cm. Within the host tree species, a clear distinction between coniferous and 24 broadleaf species was found. The next splits followed rather climatic determinants of tree